Fuse element

Abstract

To provide a fuse element capable of shutting down an electric current while suppressing formation of carbide when an abnormal current occurs.SOLUTION: A fuse element 10 includes an insulative base material 3; a conductor layer 1 provided on a surface of the base material 3; and an insulative protective layer 4 provided on a surface of the conductive layer 1. The protective layer 4 has a specific heat of 1.1 J g-1 K-1 or more and a specific gravity of 1.0 g cm-3 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a fuse element. [Background technology]

[0002] In electrical circuits, miniature fuses are used to protect against abnormal currents. An example of a miniature fuse is a chip fuse. In a chip fuse, a pair of terminal electrodes are provided on an insulating substrate, and these terminal electrodes are connected by a fusible conductor. When an abnormal current occurs, the fusible conductor melts due to the heat generated by the fusible conductor itself, or, as disclosed in Patent Document 1, due to the heat generated by a heat-generating conductor film provided between the fusible conductor and the terminal electrodes.

[0003] Flexible printed circuit boards (FPCs) are also sometimes used as miniature fuses. The structure of an FPC is disclosed, for example, in Patent Document 2, and consists of a base material with a conductive layer forming a circuit pattern on its surface. If an FPC is placed between a pair of electrodes and the electrodes are connected by the conductive layer of the FPC, the conductive layer will heat up and melt when an abnormal current occurs. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-50184 [Patent Document 2] Japanese Patent Publication No. 2001-339126 [Overview of the project] [Problems that the invention aims to solve]

[0005] In a fuse element configured to melt a conductor provided on an insulating base material, such as a chip fuse or a fuse using an FPC (FPC fuse), a member containing an organic polymer disposed near the conductor may form a carbide due to the heat generated during melting. Examples of members disposed near the conductor that may form a carbide when the conductor melts include, in an FPC, a protective layer that protects the conductor layer. In a layer containing an organic compound, such as the protective layer, the carbide formed along with the melting of the conductor includes a carbide having conductivity. The carbide having conductivity may form a conductive path between electrodes. Then, when an abnormal current flows between the electrodes, even if the conductor melts, a new conductive path is formed by the carbide, and the electric circuit cannot be interrupted. That is, the function as a fuse cannot be fully exhibited.

[0006] In view of the above, an object is to provide a fuse element that can interrupt an electric circuit while suppressing the formation of carbides when an abnormal current occurs.

Means for Solving the Problems

[0007] The fuse element of the present disclosure has an insulating base material, a conductor layer provided on the surface of the base material, and an insulating protective layer provided on the surface of the conductor layer, and the protective layer has a specific heat of 1.1 J·g -3 ·K -1 or more and a specific gravity of 1.0 g·cm -3 or more.

Effects of the Invention

[0008] The fuse element according to the present disclosure can interrupt an electric circuit while suppressing the formation of carbides when an abnormal current occurs.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing the layer structure of the fuse element. [Figure 2]FIG. 2 is an elemental distribution image showing the distribution of Si at the interface between the protective layer and the base layer in the cross section of the fuse element.

[0010] [Description of Embodiments of the Present Disclosure] First, the embodiments of the present disclosure will be listed and described. The fuse element of the present disclosure has an insulating base material, a conductor layer provided on the surface of the base material, and an insulating protective layer provided on the surface of the conductor layer. The protective layer has a specific heat of 1.1 J·g -1 ·K -1 or more and a specific gravity of 1.0 g·cm -3 or more.

[0011] If the above fuse element is provided in the middle of an electric circuit to be interrupted when an abnormal current occurs, and the circuit current is configured to flow through the conductor layer of the fuse element, when an abnormal current occurs and heat generation occurs in the conductor layer, the conductor layer melts, thereby interrupting the electric circuit. Here, the protective layer provided on the surface of the conductor layer has a specific heat of 1.1 J·g -1 ·K -1 or more and a specific gravity of 1.0 g·cm -3 or more, so that it has a large heat capacity. Therefore, even when the conductor layer generates heat during melting, the temperature of the protective layer is unlikely to rise. By suppressing the temperature rise of the protective layer, it is difficult for carbides to be formed in the protective layer, and it is unlikely that the formation of a conductive path through the conductive carbides will prevent the circuit from being interrupted.

[0012] The fuse element is preferably configured using a flexible printed circuit board, and the base material and the conductor layer of the fuse element are each composed of the base layer and the metal foil of the flexible printed circuit board. By using a flexible printed circuit board, a small-sized fuse element can be formed simply and at low cost. At this time, by configuring the protective layer using a material having a predetermined specific heat and specific gravity, it is possible to suppress the formation of carbides in the protective layer and the associated failure of the interruption of the electric circuit when the metal foil melts.

[0013] The protective layer may contain at least one of a silicone resin and a modified silicone resin. Among various resin materials, silicone resins and modified silicone resins have relatively large specific gravity and specific heat, and are excellent in suppressing the temperature rise of the protective layer and the formation of carbides accompanying the same when the conductor layer is blown. Further, when the protective layer contains a silicone resin or a modified silicone resin, silicon oxide (SiO x ) is formed at the interface between the protective layer and the conductor layer as the conductor layer generates heat, thereby further suppressing the formation of carbides in the protective layer.

[0014] The protective layer may contain a heat-insulating filler. The heat-insulating filler improves the specific heat of the protective layer and exhibits a high effect in suppressing the temperature rise of the protective layer and the formation of carbides accompanying the same when the conductor layer is blown.

[0015] The protective layer may include foam cells. The foam cells improve the specific heat of the protective layer and exhibit a high effect in suppressing the temperature rise of the protective layer and the formation of carbides accompanying the same when the conductor layer is blown. The foam cells can be easily formed by mixing a foaming agent into the protective layer and heating it.

[0016] [Details of Embodiments of the Present Disclosure] Hereinafter, the fuse element according to the embodiment of the present disclosure will be described in detail with reference to the drawings. In this specification, various physical property values are values measured in the air at room temperature (generally from 20°C to 25°C). Further, that a certain component is the main component of a certain material refers to a state in which the component occupies 50% by mass or more of the entire material.

[0017] [Structure of FPC Fuse] First, as an example of a fuse element according to this disclosure, an FPC fuse constructed using a flexible circuit board (FPC) will be described. Figure 1 shows the layer configuration of a cross-section of an FPC fuse 10 according to one embodiment of this disclosure. The FPC fuse 10 is used to connect a pair of electrodes at a point in the middle of an electrical circuit provided on a circuit board.

[0018] As shown in Figure 1, the FPC fuse 10 has a structure in which multiple layers are laminated. Specifically, the FPC fuse 10 has a base layer (substrate) 3 and a metal foil (conductor layer) 1 that covers at least one surface of the base layer 3. The base layer 3 and the metal foil 1 are bonded together by an adhesive layer 2. An insulating protective layer 4 is provided on the surface of the metal foil 1. The protective layer 4 may be fixed to the surface of the metal foil 1 via an adhesive layer (not shown in the figure). Such a laminated structure is conventionally used in general-purpose FPCs.

[0019] The base layer 3 is constructed as an insulating substrate. The material constituting the base layer 3 is not particularly limited, but flexible polymer materials commonly used as base layers in FPCs, such as polyethylene terephthalate (PET) or polyimide (PI), can be suitably used. For the metal foil 1, it is preferable to use copper foil, which is a material commonly used in FPCs. The thickness of the metal foil 1 should be 10 μm or more from the viewpoint of ensuring sufficient conductivity. On the other hand, the thickness of the metal foil 1 should be 50 μm or less from the viewpoint of making it easier to break even with a small amount of heat generated when an abnormal current flows. The constituent materials of the adhesive layer 2 and the adhesive optionally placed between the metal foil 1 and the protective layer 4 are also not particularly limited, and adhesives such as acrylic, epoxy, urethane, and silicone can be used.

[0020] The protective layer 4 covers the surface of the metal foil 1 and is provided as the outermost layer of the FPC fuse 10. The protective layer, also called a coverlay, plays a role in insulating and protecting the surface of the metal foil in the FPC. As will be explained in detail later, in the FPC fuse 10 according to this embodiment, the protective layer 4 has predetermined physical properties. As will be described later, the fuse element of this disclosure can be configured in a form other than the FPC fuse 10, but by using the FPC fuse 10, flexibility can be given to the fuse element, and the fuse element can be easily formed using FPC, which can be mass-produced at low cost.

[0021] <Composition of the protective layer> In the FPC fuse 10 according to this embodiment, the protective layer 4 has predetermined physical properties. That is, the protective layer 4 has 1.0 J·g -1 ·K -1 The specific heat is as described above, and 1.0 g·cm³. -3 It has at least one of the above specific gravities. Preferably, it has both specific heat and specific gravity.

[0022] The heat capacity of a material increases as its specific heat and specific gravity increase. Therefore, in the FPC fuse 10, the greater the specific heat and specific gravity of the protective layer 4, the greater its heat capacity, even if the protective layer 4 is formed to the same thickness. This makes it more difficult for the temperature of the protective layer 4 to rise when it is heated.

[0023] Here, we consider a configuration in which an FPC fuse 10 is placed between a pair of electrodes in the middle of an electrical circuit, and the electrodes are electrically connected by a metal foil 1 covered with a protective layer 4, and an abnormal current (abnormally large current) occurs between the electrodes. When the abnormal current of the electrical circuit flows through the metal foil 1, the metal foil 1 heats up due to electrical resistance. When the temperature of the metal foil 1 reaches a temperature above its melting point or sublimation point due to its own heat generation, the metal foil 1 melts and breaks. When the metal foil 1 melts and breaks, the conduction through the metal foil 1 in the electrical circuit is interrupted, and current stops flowing in the electrical circuit. As a result, the electrical circuit is protected from the abnormal current.

[0024] As described above, the metal foil 1 generates heat due to the occurrence of an abnormal current, and the heat generated in the metal foil 1 is also transferred to the adjacent protective layer 4. As a result, the protective layer 4 is heated. When the protective layer 4 is heated to a high temperature, carbides may be formed from the organic material that makes up the protective layer 4. Some of the carbides that are formed may be conductive. If conductive carbides are formed in the protective layer 4, a conductive path may be formed through the conductive carbides at the location where the conductivity of the metal foil 1 was interrupted by melting. As a result, the conductivity of the metal foil 1 may no longer be interrupted, or the conductivity that was interrupted by melting the metal foil 1 may be reformed. Consequently, even though the metal foil 1 is melted, the conductivity in the electrical circuit may not actually be interrupted, or the conductivity that was interrupted may be reformed, making it impossible to protect the electrical circuit from abnormal currents.

[0025] However, the protective layer 4 of the FPC fuse 10 according to this embodiment is 1.0 J·g -1 ·K -1 The above specific heat, and / or 1.0 g·cm³ -3 Due to its specific gravity, it has a large heat capacity and its temperature does not rise easily. Therefore, even if the adjacent metal foil 1 generates heat due to the occurrence of an abnormal current, the temperature rise and the resulting carbide formation are unlikely to occur in the protective layer 4. Thus, even if the metal foil 1 is melted by an abnormal current, it is unlikely that a conductive path will be formed due to the contribution of conductive carbides formed in the protective layer 4, and the electrical circuit can be properly protected from abnormal currents.

[0026] The specific heat of protective layer 4 is 1.1 J·g -1 ·K -1 The above, and also 1.3J·g -1 ·K -1 It is even more preferable if the above is true. Also, the specific gravity of the protective layer 4 is 1.1 g·cm³. -3 The above, and also 1.2 g·cm -3 It is even more preferable if the above is true. Particularly preferable, the protective layer 4 is 1.1 J·g -1 ·K -1The specific heat is as described above, and 1.0 g·cm³. -3 It is preferable that the material possesses both the specific heat and specific gravity mentioned above. While there are no particular upper limits on the specific heat and specific gravity of the protective layer 4, for materials that can be practically applied as a protective layer 4 for protecting the metal foil 1, the specific heat is generally 3.0 J·g. -1 ·K -1 The following is true, and the specific gravity is 2.0 g·cm³. -3 The following applies:

[0027] The thickness of the protective layer 4 is not particularly limited, but from the viewpoint of providing sufficient protection to the metal foil 1 and increasing the heat capacity of the protective layer 4 through volumetric effects, it is preferable to make it 30 μm or more. On the other hand, from the viewpoint of increasing the flexibility of the FPC fuse 10, the thickness of the protective layer 4 is preferable to be 1 mm or less.

[0028] The specific constituent materials of the protective layer 4 are not particularly limited as long as they have the predetermined physical properties described above, but it is preferable that they consist mainly of an organic polymer. Suitable organic polymers that can be used as constituent materials for the protective layer 4 include silicone resins, modified silicone resins, urethane resins, and fluororesins such as polytetrafluoroethylene. One type of organic polymer may be used, or two or more types may be used in combination.

[0029] Among the various organic polymers listed above, it is particularly preferable to use at least one of silicone resin and modified silicone resin as the organic polymer constituting the protective layer 4. Preferably, the main component, and even the entirety, of the organic polymer constituting the protective layer 4 is silicone resin and / or modified silicone resin. Examples of modification groups contained in the modified silicone resin include amino groups and carboxyl groups.

[0030] Silicone resins and modified silicone resins (hereinafter referred to collectively as silicone resins unless otherwise specified) have relatively high specific heat and specific gravity among various organic polymers, thus providing a large heat capacity and making it easier to suppress carbonization of the protective layer 4. Furthermore, in an FPC fuse 10 provided with a protective layer 4 containing silicone resin, when the metal foil 1 generates heat, silicon oxide (SiO₂) forms in the interface region of the protective layer 4 facing the metal foil 1. x A silicon oxide is formed. This formation of silicon oxide effectively suppresses the formation of carbides in the protective layer 4 due to the heat generated by the metal foil 1. This is thought to be because the formed silicon oxide has high thermal insulation properties and a high melting point. Thus, the formation of carbides in the protective layer 4 due to the heat generated by the metal foil 1 is effectively suppressed by both the effect of the protective layer 4 containing silicone resin, which provides a large heat capacity, and the effect of the formation of silicon oxide at the interface on the metal foil 1 side. Note that the silicon oxide formed at the interface of the protective layer 4 contains SiO x This includes not only pure oxides having the above composition, but also compounds that contain other elements such as C in smaller amounts than O, in addition to Si and O.

[0031] Furthermore, it is preferable that the protective layer 4 contains a thermal insulation filler in addition to the organic polymer. This is because the specific heat of the protective layer 4 can be easily increased by including a thermal insulation filler. Generally, a thermal insulation filler with a thermal conductivity of 10 W / m·K or less should be used. The specific type of thermal insulation filler is not particularly limited, but examples include inorganic particles such as calcium carbonate, titanium dioxide, and silica, and hollow particles such as glass bubbles. The amount of thermal insulation filler in the protective layer 4 is not particularly limited, but from the viewpoint of enhancing the effect of improving specific heat, for example, it should be set to 5% by mass or more as a percentage of the entire protective layer 4. On the other hand, from the viewpoint of not impairing the properties of the protective layer 4 exhibited by the polymer material, it is preferable to set it to 30% by mass or less.

[0032] From the viewpoint of increasing specific heat, the protective layer 4 may contain foam cells instead of, or in addition to, the above-mentioned heat-insulating filler. Foam cells are bubbles formed inside the protective layer 4 by the foaming of the foaming agent, and increase the specific heat of the protective layer 4 as a whole. In order to include foam cells in the protective layer 4, the foaming agent should be mixed into the material when forming the protective layer 4, and after forming it into a film, it should be heated to cause the foaming agent to foam.

[0033] The type of blowing agent used to form the foam cell is not particularly limited, but it is preferable to use a blowing agent consisting of an azo compound, a nitroso compound, or a hydrazine derivative. These compounds often generate nitrogen gas without containing water (water vapor) during foaming, and the remaining water inside the protective layer 4 prevents water from adhering to the rupture site of the metal foil 1 and its vicinity when an abnormal current occurs, thus preventing the formation of a conductive path through water. Examples of azo compounds include azodicarbonamide and barium azodicarboxylate. Examples of nitroso compounds include N,N'-nitrosopentamethylenetetramine, and examples of hydrazine derivatives include hydrazodicarbonamide and 4,4'-oxybis(benzenesulfonylhydrazide). One type of blowing agent may be used, or two or more types may be used in combination. The content of the blowing agent in the protective layer 4 is not particularly limited, but for example, from the viewpoint of enhancing the effect of improving the specific heat by the foam cell, it is sufficient to have a content of 5% by mass or more in relation to the entire protective layer 4. On the other hand, from the viewpoint of maintaining high mechanical strength of the protective layer 4, it is preferable to keep it at 20% by mass or less.

[0034] <Other forms> In the above, as an example of an embodiment of the present disclosure, a configuration in which the protective layer 4 of the FPC fuse 10 has predetermined physical properties was described. However, the fuse element of the present disclosure is not limited to such a configuration.

[0035] The fuse element of this disclosure is not limited to an FPC fuse, but may have an insulating substrate, a conductive layer provided on the surface of the substrate, and an insulating protective layer provided on the surface of the conductive layer. The protective layer is 1.0 J·g -1 ·K -1 The specific heat is as described above, and 1.0 g·cm³. -3 The specific gravity shall be such that it has at least one of the above. Preferably, the protective layer has a specific gravity of 1.1 J·g -1 ·K -1 The specific heat is as described above, and 1.0 g·cm³. -3 It is preferable that the specific gravity is as described above. The substrate, conductor layer, and protective layer constituting the above laminated structure correspond to the base layer 3, metal foil 1, and protective layer 4, respectively, in the FPC fuse 10. In addition to the form using FPC, other forms of fuse elements having the above laminated structure include those having a pattern fuse provided as a circuit pattern on a printed circuit board, and a chip fuse mounted on a printed circuit board. It is preferable that the layer in direct contact with the conductor layer is made of a protective layer having the specific heat and specific gravity as described above, but the protective layer may be provided on the surface of the conductor layer via another layer. For example, as in the sample used in later embodiments, the protective layer may cover the conductor layer via a substrate (base layer) and / or an adhesive layer.

[0036] Furthermore, in a fuse element, not only the protective layer, but also the adhesive layer, the substrate, and other layers adjacent to the conductor layer on the opposite side of the protective layer, or the layer interposed between the protective layer and the conductor layer, may also be provided with the specified specific heat and / or specific gravity. In this case, when the conductor layer generates heat, the formation of carbides can be suppressed not only in the protective layer, but also in the adhesive layer and the substrate. [Examples]

[0037] Examples are shown below. However, the present invention is not limited to these examples.

[0038] <Sample preparation> An FPC fuse was prepared in which a base layer was provided on both sides of a copper foil via an adhesive layer, and a protective layer was provided on one surface of these base layers. In this FPC fuse, the base layer is made of 25 μm thick polyimide resin, the adhesive layer is made of 10 μm thick epoxy resin, and the conductor layer is made of 35 μm thick copper foil. A 50 μm thick protective layer was fabricated using the following resins A to D. In addition, tapes A and B were attached as alternative protective layers.

[0039] The types of materials used to form the protective layer are as follows: • Resin A: Silicone resin (Three Bond "1537E") • Resin B: Silicone resin (Toray DOW Corporation's "CV9204-20") to which 10% by mass of calcium carbonate (CaCO3) is added. • Resin C: Epoxy resin (Three Bond "2272H") • Resin D: EVA resin (Henkel's "LOCTITE Hot Melt Adhesive") Tape A: PVC tape (Nitto Denko Corporation's "Wire Harness Vinyl Tape No. 2117TVH"), 0.07mm thick Tape B: Fluororesin tape (AGF-100A, manufactured by Chuko Chemical Industries Co., Ltd.), 0.13mm thick

[0040] <Testing Method> The fabricated FPC fuses were connected to a DC power supply, and a current of 2.5A was passed through them for 60 seconds to melt the copper foil. Afterward, the appearance of the protective layer was visually inspected to evaluate whether or not carbides had formed. Furthermore, for the FPC fuses using resin A, energy-dispersive X-ray spectroscopy (SEM-EDX) was performed on the cross-section after the copper foil melted by current to observe the spatial distribution of constituent elements.

[0041] <Result> Table 1 below summarizes the constituent materials of the protective layer and whether or not carbide formation occurred.

[0042] [Table 1]

[0043] According to Table 1, in FPC fuses where the protective layer is composed of resins A and B and tape B, no carbides are formed in the protective layer when the copper foil is melted. The materials constituting the protective layer have a strength of 1.1 J·g -1 ·K -1 The specific heat is as described above, and 1.0 g·cm³. -3 It possesses both of the above specific gravities. Therefore, as a protective layer to be provided on the fuse element, 1.1 J·g -1 ·K -1 The specific heat is as described above, and 1.0 g·cm³. -3 By using materials with the above specific gravity, it is possible to interrupt the circuit by melting the conductor layer while avoiding carbonization of the protective layer when an abnormal current occurs.

[0044] Figure 2 shows the spatial distribution of Si at the interface between the protective layer and the base layer of an FPC fuse with a protective layer made of silicone resin, obtained by SEM-EDX measurement. Areas shown in bright colors indicate higher Si concentrations. In the image, the darker upper layer corresponds to the base layer, and the lower layer, where regions with high Si concentrations are unevenly distributed, is the protective layer. At the interface between the base layer and the protective layer, a region with high uniformity and high Si concentration is created on the protective layer side, labeled "interface layer" in the image. Although the image is omitted, it was confirmed that O is also distributed with high uniformity and high concentration in this interface layer region. In other words, at the interface where the protective layer faces the conductor layer via the base layer, silicon oxide (SiO₂) is produced after heating during the melting of the conductor layer. x This suggests that ) is being generated.

[0045] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Explanation of Symbols]

[0046] 10 FPC fuses (fuse elements) 1. Metal foil (conductor layer) 2 Adhesive layer 3. Base layer (substrate) 4 protective layer

Claims

1. A fuse element provided by connecting a pair of electrodes, A flexible printed circuit board is constructed using a metal foil, which serves as a conductive layer for electrically connecting the pair of electrodes, with an insulating base layer provided on both sides of the foil, and the base layer and the metal foil bonded together by an adhesive layer. An insulating protective layer is provided on one surface of the base layer and covers the surface of the metal foil as the conductor layer via the base layer and a layer of adhesive including at least the adhesive layer. The base layer and the protective layer cover the surface of the metal foil at the location where the metal foil melts when a large current is generated between the pair of electrodes. The protective layer is 1.1 J·g －１ ・K －１ The specific heat is as described above, and 1.0 g / cm³. －３ A fuse element having the above specific gravity.

2. The fuse element according to claim 1, wherein the base layer comprises at least one of polyethylene terephthalate and polyimide.

3. The fuse element according to claim 1 or claim 2, wherein the protective layer contains a heat insulating filler.

4. The fuse element according to any one of claims 1 to 3, wherein the protective layer includes foam cells.

5. The specific heat of the protective layer is 1.3 J·g. －１ ・K －１ The fuse element according to any one of claims 1 to 4.

6. The fuse element according to any one of claims 1 to 5, wherein the protective layer comprises a urethane resin or a fluororesin.

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